Very basic group chats, tested and working with nTox.

Please wait until the tox.h API is updated before integrating it into
your clients.

nTox:
/g
creates a new group chat

/i friendnum groupnum
invite friendnum to groupnum

/z groupnum message
send message to groupnum

NOTE: group chats currenly might not handle packet loss well if there are less than 6 participants.
Merge branch 'master' of https://github.com/irungentoo/ProjectTox-Core